Remove long-obsolete `is_blocklisted_fn` mechanism. #413

Job	Run time
Lint	5m 58s
Test (macOS-latest, x86_64-apple-darwin)	22m 36s
Test (windows-2022, x86_64-pc-windows-msvc)	27m 4s
Test (ubuntu-24.04, x86_64-unknown-linux-gnu)	16m 26s
cargo-deny	1m 2s
Test (ubuntu-24.04, aarch64-linux-android, x86_64-unknown-linux-gnu)	7m 53s
test_success	3s
	1h 21m 2s

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